You can optimize your Facebook social sharing image sizes to generate great previews.
Use images that are at least 1200 x 630 pixels for the best display on high resolution devices. At the minimum, we require using images that are 600 x 315 pixels to display link page posts with larger images.
Here’s an example from Facebook:
Once you setup the social sharing settings, any social share will pull from that customized content automatically.
We do not allow you to upload any images smaller than 600 x 315 pixels so that your Facebook sharing can be fully optimized.
Try to keep your images as close to 1.91:1 aspect ratio as possible to display the full image in News Feed without any cropping on mobile phones.